Segmental assembly of fibronectin matrix requires rap1b and integrin α5

Dev Dyn. 2013 Feb;242(2):122-31. doi: 10.1002/dvdy.23909. Epub 2013 Jan 7.

Abstract

Background: During segmentation of the zebrafish embryo, inside-out signaling activates Integrin α5, which is necessary for somite border morphogenesis. The direct activator of Integrin α5 during this process is unknown. One candidate is Rap1b, a small monomeric GTPase implicated in Integrin activation in the immune system.

Results: Knockdown of rap1b, or overexpression of a dominant negative rap1b, causes a mild axis elongation defect in zebrafish. However, disruption of rap1b function in integrin α5(-/-) mutants results in a strong reduction in Fibronectin (FN) matrix assembly in the paraxial mesoderm and a failure in somite border morphogenesis along the entire anterior-posterior axis. Somite patterning appears unaffected, as her1 oscillations are maintained in single and double morphants/mutants, but somite polarity is gradually lost in itgα5(-/-) ; rap1b MO embryos.

Conclusions: In itgα5(-) (/) (-) mutants, rap1b is required for proper somite border morphogenesis in zebrafish. The loss of somite borders is not a result of aberrant segmental patterning. Rather, somite boundary formation initiates but is not completed, due to the failure to assemble FN matrix along the nascent boundary. We propose a model in which Rap1b activates Integrin/Fibronectin receptors as part of an "inside-out" signaling pathway that promotes Integrin binding to FN, FN matrix assembly, and subsequent stabilization of morphological somite boundaries.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cell Polarity / physiology
  • Cleavage Stage, Ovum / physiology*
  • Extracellular Matrix / metabolism*
  • Fibronectins / metabolism*
  • Gene Knockdown Techniques
  • Image Processing, Computer-Assisted
  • Immunohistochemistry
  • In Situ Hybridization
  • Integrin alpha5 / genetics
  • Integrin alpha5 / metabolism*
  • Microscopy, Fluorescence
  • Morphogenesis / physiology
  • Morpholinos / genetics
  • Signal Transduction / physiology*
  • Somites / embryology
  • Zebrafish / embryology*
  • Zebrafish Proteins / metabolism*
  • rap GTP-Binding Proteins / genetics
  • rap GTP-Binding Proteins / metabolism*

Substances

  • Fibronectins
  • Integrin alpha5
  • Morpholinos
  • Zebrafish Proteins
  • Rap1b protein, zebrafish
  • rap GTP-Binding Proteins